Remove slash command listener, make PersonaManagers accessible

[dlqqq]

Description

• Removes the slash command listener from this package.

• Removes backend handling of the /refresh-personas command as it will be implemented in Add existing chat commands jupyter-ai-chat-commands#1.

• Makes PersonaManager instances accessible to other extensions by binding the dictionary to self.settings['jupyter-ai']['persona-managers'].

• Makes PersonaManager._refresh_personas() a public method as it will be called by jupyter_ai_chat_commands.

Technical details

jupyter_ai_chat_commands will do the following in its extension to handle /refresh-personas:

1. Asynchronously poll until self.settings['jupyter-ai']['router'] is available.
2. Add a slash command listener. On each slash command call:
3. Asynchronously poll until persona_manager := self.settings['jupyter-ai']['persona-managers'][room_id] are accessible.
4. Call persona_manager._refresh_personas() in a background task.

[3coins]

LGTM!

[dlqqq]

@3coins Thanks! Merging & releasing as v0.0.2.